1. Field of the Invention
The invention relates to a system and method for characterizing the quality of a semiconductor device and, more particularly, to a system and method for characterizing the quality of the interface between a silicon and a gate insulator in a MOS device.
2. Description of the Related Art
Metal-oxide-semiconductor transistors (hereinafter referred to as MOS devices) are the most widely used and most important transistors in the Ultra-Large-Scale-Integrated (ULSI) circuits using the silicon semiconductor crystal. Various kinds of integrated circuits (ICs) such as microprocessors used in personal computers are usually constituted by up to several millions of MOS devices. Therefore, the properties of the MOS devices have to be well controlled so as to obtain an integrated circuit with good performance. For example, it is well known that the lattice defects, impurities, interface state densities (Dit) and minority carrier lifetime near the gate insulator/silicon interface, are closely related to the quality of the gate insulator and the performance of a MOS device. As a result, it is very important to exactly measure the defects, impurities, interface state densities (Dit) and minority carrier lifetime near the gate insulator/silicon interface in MOS devices.
Conventional methods such as the high/low frequency capacitance-voltage analysis, conductance method, charge-pumping method, and transient capacitance-time Zerbst analysis, etc., have been successfully used to measure the interface state densities and minority carrier lifetime of MOS devices with relatively thick gate insulator. However, when the line width has been reduced to 0.13 to 0.09 microns in the advanced ULSI technology, the thickness of the gate insulator in a MOS device is in the range of 15 to 30 angstroms, which is about the thickness of 3 to 6 layers of atoms. The ultra-thin gate insulator with such small thickness may result in significant leakage current tunneling through the gate insulator, thereby increasing series resistance of MOS capacitors. The significant series resistance in MOS devices due to the ultra-thin gate insulator complicates the analysis and causes the modeling based on the above measurement technologies to be difficult. As a result, it is necessary to develop a novel and simpler method for measuring the defects, impurities, interface state densities, and minority carrier lifetime near the gate insulator/silicon interface in the MOS devices with ultra-thin gate insulator
To solve the above-mentioned problems, the invention provides a characterization system and method utilizing the characteristics of great gate tunneling currents in the MOS device with ultra-thin gate insulator. The minority carrier lifetime near the gate insulator/silicon interface in the MOS device is obtained by measuring the temporal electroluminescenct signal corresponding to the silicon bandgap energy. The characterization system and method can be used to investigate the parameters related to the quality of the gate insulator/silicon interface, such as lattice defects, impurities, interface state densities.
To achieve the above-mentioned object, a method to characterize the gate insulator/silicon interface quality in the MOS device with ultra-thin gate insulator includes the steps of applying a current to the MOS device through the gate; detecting at least one electroluminescent signal corresponding to the silicon bandgap energy after the current flows through the MOS device; and outputting the electroluminescent waveform in the time domain. The minority carrier lifetime can be extracted from the temporal electroluminescent waveform. The quality of the gate insulator/silicon interface in the MOS device is determined by analyzing the minority carrier lifetime in silicon.
To implement the above-mentioned method, a characterization system may include a current source, a photodetector and an output sub-system. The output sub-system may include a gate integrator and boxcar averager, a gate scanner and an X-Y recorder. The current source applies at least one current to the MOS device. The photodetector detects at least one electroluminescent signal corresponding to the silicon bandgap energy after the current flows through the MOS device. The gate integrator and boxcar averager receives the electroluminescent signals, integrates the signals during the gated period, and averages the received electroluminescent signals over many shots of the injection current. The gate scanner controls the position of the gate in the gate integrator and boxcar averager in the time domain, so that the gate can scan in the time domain to allow the retrieval of entire temporal electroluminescent waveform. The X-Y recorder records the voltage signals output from the gate scanner as the time axis, and records the voltage signals output from the gate integrator and boxcar averager as the intensity of the electroluminescent signals, to obtain the electroluminescent waveform in the time domain. According to the measured temporal electroluminescent waveform, the minority carrier lifetime near the gate insulator/silicon interface can be obtained.
The current supplied from the current source may be a square wave or a pulse. The electroluminescent signal from the photodetector may be amplified by an amplifier. The photodetector may be an InGaAs or a germanium photodetector. The bandwidths of the current source, photodetector, amplifier and gate integrator and boxcar averager have to be greater than 10 MHz.
The output sub-system also may be a combination of an amplifier and an oscilloscope. Under the condition that the amplification of the amplifier is great enough and the bandwidths of the amplifier and oscilloscope are large enough ( greater than 10 MHz), the oscilloscope may directly display the temporal electroluminescent waveform.